Long-term exposure to fine particulate matter and dementia incidence: A cohort study in Hong Kong

Recent studies suggested that long-term exposure to fine particulate matter (PM_2.5) was related to a higher risk of dementia incidence or hospitalizations in western populations, but the evidence is limited in Asian cities. Here we explored the link between long-term PM_2.5 exposure and dementia incidence in the Hong Kong population and whether it varied by population sub-group. We utilized a Hong Kong Chinese cohort of 66,820 people aged ≥65 years who were voluntarily enrolled during 1998-2001 and were followed up to 2011. Prevalent dementia cases were excluded based on the face-to-face interview at baseline. We ascertained the first occurrence of hospitalization for all-cause dementia and major subtypes during the follow-up period. We assessed PM_2.5 concentrations using a satellite data-based model with a 1 × 1 km² resolution on the residential address. Cox proportional hazards models were adopted to estimate associations of annual mean PM_2.5 exposure with dementia incidence, adjusting for potential confounders. We identified 1183 incident cases of all-cause dementia during the follow-up period, of which 655 (55.4%) were cases of Alzheimer's disease, and 334 (28.2%) were those of vascular dementia. We found a positive association between annual mean PM_2.5 exposure and all-cause dementia incidence in the fully adjusted model. The estimated hazard ratio was 1.06 (95% confidence interval (CI): 1.00, 1.13) per every 3.8 μg/m³ increase in annual mean PM_2.5 exposure. And the estimated HRs for Alzheimer's disease and vascular dementia were 1.03 (95% CI: 0.94, 1.12) and 1.09 (95% CI: 0.98, 1.22), respectively. We did not find effect modifications by age, sex, BMI, hypertension, diabetes, or heart disease on the associations. Results suggest that long-term exposure to PM_2.5 is associated with a higher risk of dementia incidence in the Asian population.